Out of those 2, I'd put more faith in the JG out of the box. JG guns usually required a bit of preventative maintenance out of the box to ensure longevity, but generally can be run for thousands of rounds totally stock.
Krakens are very popular guns, but are better as an upgrade platform than stock. Upgrading a Kraken both internally and externally can give someone a fully metal and wood gun with top notch performance for about the price of a new Tokyo Marui AK.
Out of the box, some people experience surprising performance and reliability out of their Krakens. Others encounter problems shortly after getting them. Generally, the problems are minor for someone who knows how to fix them, but for a noob who typically buys a Kraken as a first gun, the repair can be intimidating.
So IMO, if you like the look of the Thundermaul (I'm not crazy about it, but I like it), then go for it. While some JG guns have some issues, they're generally quite good, and more reliable than a Kraken.
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